Determining the mechanisms behind the mesenchymal stem cell response to strontium apatite-wollastonite glass ceramic

Abstract

The aim of this project was to determine the effects of strontium addition to Apatite Wollastonite Glass-Ceramic (SrAWGC) on human mesenchymal stem/stromal cells (MSCs), and to identify through which mechanisms these effects operated. SrAWGC has a molar composition of 35.4SiO2-7.1P2O5-0.4CaF2-7.1MgO-(49.9-x)CaO-xSrO, where x = 0, 6.2, 12.5, 18.7, 24.9, 37.4. Neutron diffraction, Magic Angle Spinning Nuclear Magnetic Resonance and Raman spectroscopy found that Sr substitution did not alter the short-range order, but at the medium range the percentage of Q3 silicate decreased, alongside a significant increase in the density of the glass. The glass compositions were heat treated into SrAWGC discs using a polymer slurry casting method, with high strontium compositions showing altered surface topographies. SrAW glasses released strontium linearly with increasing strontium content, whereas the SrAWGC discs released both increasing concentrations of strontium and silicon with strontium content, suggesting increased glass-ceramic dissolution with Sr substitution. The 12.5 Mol% SrAW glass conditioned media and 6.2 mol% SrAWGC discs induced an increase in MSC cell number. The 0 and 12.5 mol% SrAWGC discs significantly raised the expression of genes associated with inflammatory response (determined with RNA sequencing), compared with cells exposed only to the ionic release products of the material. The addition of strontium to the material was found to have a relatively small effect, but did slightly increase the inflammatory gene expression induced by the discs. An in vivo study found that the MSCs conditioned to have raised inflammatory gene expression by the discs did not promote a sustained inflammatory response. The discs and ionic dissolution products (with 12.5 mol% Sr) were found to increase the expression of proliferative and survival-oriented gene groupings, such as K-Ras signalling. A K-Ras inhibitor abrogated the previously described SrAW glass associated rise in cell number